Mecanum or Swerve?

[TEE]

Originally Posted by sdcantrell56

We're using 8wd tank drive with 6 motors this year (4cims and 2 FP's)


Any team only using 2 cims in the drive this year is seriously hurting themselves

This year, we had a tank drive with 2 omni's in the back, so the robot would turn around its front (where the ball is), and we only used 2 cims. We could have added two more, but two seemed to be working fine; we could push well, and we could move around okay. We didn't end up adding two more because of the added weight (which would slow our hanging down).

[Chris is me]

Originally Posted by joek

but, most tank drives use only 2 drive motors, whereas omni and mechanum ALWAYS use 4, so there is pore power being delivered, despite the 30% decrease, we have mechanum, and were able to push around tank drives like it was notheing

Very few respectable tank drives use only 2 motors, and very few use relatively low traction wheels like KoP wheels that your mecanum drive could push. I guess if they used the wheels in the KoP you could push them around, but that's hardly the level of competition you have to play defense against.

A mecanum drive is limited by traction faster than a tank drive, thus, it will have less "pushing power" in most situations.

[Ether]

Originally Posted by Chris is me

A mecanum drive is limited by traction faster than a tank drive, thus, it will have less "pushing power" in most situations.

Yes! In the pure forward and reverse directions, a mecanum wheel's pushing force is limited by traction, not by a vector reduction in the amount of available force.

Even if a mecanum wheel's rollers were made of the exact same material as a standard wheel of the same wheel diameter, the mecanum would lose traction before the standard wheel would.

This is because the reaction force of the floor (carpet) on the mecanum wheel's roller is larger than the reaction force on a standard wheel, given the same driving torque on the wheel.


~

[steelerborn]

I really like the swerve drives over mecanum drives.
I am working on a cad of an offseason swerve system right now.
It should be posted soon.

[buildmaster5000]

Originally Posted by steelerborn

I am working on a cad of an offseason swerve system right now.
It should be posted soon.

If you could PM me when its up, that would be great!! We have been stuck with the 221 modules because we lack the resources to design one ourselves

[ADHDassassin]

Originally Posted by =Martin=Taylor=

In my six years of competing in FIRST I don't remember a single mecanum robot ever dominating a competition.
.

I'm not exactly sure how my team did this year but we dominated FIRST Overdrive in 2008 with a mecanum robot, before FIRST Nationals we had a 30-1-0 record and two regional victories. It was an incredible design for turning around that track as we could essentially rotate around are front left wheel to make incredibly sharp turns. It also helped that we had a driver that also flew RC planes at a national level.

I understand that Lone Star and Bayou are considered to be "easier" regionals but we controlled that competition from our very first match. At nationals we had some code and design issues that prevented us from success... We gave in to the temptation to fix something that was already working.


But overall I love the mecanum drive train and watching one work is a beautiful demonstration of force vectors

[Jeffy]

If you want an omnidirectional drivetrain, it appears that swerve would be the best because it gives omnidirectional motion with better traction and without the power loss of mecanum.
However, our meccanum drivetrain has served us very well this year. When we decided we wanted to have omni directional capabilites they were our best option because our team is not capable of building a successful swerve in 2 weeks.
The mecanum does have (atleast) one advantage, swerve has a lag while the pods turn. One other might be weight. If you direct drive 6" mecanums then it should surely be lighter than 4 (or 6) swerve pods, chain, and sterring assemblies. This did not prove to be the case for us this year because we are chain driving 4 8" wheels with 4 toughboxes.

For a game like breakaway where pushing isn't a factor unless your playing a defensive strategy, you really can't go wrong with either.

[sparrowkc]

Originally Posted by Jeffy

For a game like breakaway where pushing isn't a factor unless your playing a defensive strategy...

I would disagree with that. A great offensive robot can be easily shut down if it can't push back.

[Jeffy]

Originally Posted by sparrowkc

I would disagree with that. A great offensive robot can be easily shut down if it can't push back.

There are two goals, and hopefully more than one ball in your zone, so I don't think that you would be needing to push another robot our of the way.
However, there is one situation that I see you needing to push another robot while in your home zone: If they have hearded all of the balls in the zone into one corner and are guarding them. In which case, the only way to really push them would be into the wall. And it leaves the rest of the zone open to the offensive robot.

I would love to hear why you think what you do. Our team had a large discussion about the need for an omni drive vs. a tank drive at the beggining of the year.

[Tom Line]

Originally Posted by Jeffy

There are two goals, and hopefully more than one ball in your zone, so I don't think that you would be needing to push another robot our of the way.
However, there is one situation that I see you needing to push another robot while in your home zone: If they have hearded all of the balls in the zone into one corner and are guarding them. In which case, the only way to really push them would be into the wall. And it leaves the rest of the zone open to the offensive robot.

I would love to hear why you think what you do. Our team had a large discussion about the need for an omni drive vs. a tank drive at the beggining of the year.

Easy answer. We knew from our testing and from past experience that a robot defending you was going to try to push you all over the place.

Exactly that happened in the Michigan State Championships to us. Thunderchickens tried to play defense on us. They have traction when they want to, and can push very well. We out-pushed them somewhat and managed to wedge them in the goal for a short time, but they still kept our robot down to scoring only 5 balls.

Their drivers understood that to keep the other guy from scoring, you simply push his back corner so he can't aim. Or push him into the wall so he can't turn. Or pull in front of the goal if he can't push at all, then he's done.

Mechanum and omni look great as concepts, but when the rubber hits the road all it takes is one good traction bot to completely shut them down.

[sparrowkc]

I'm not so much saying that an offensive robot needs to push other robots, just that a slippery bot is more susceptible to being pushed into a corner or into an unfavorable position. Anyways, I think our ideas of offense are different. We play mostly from the middle zone, and that means competing for the space under the ball return and fighting for individual balls and clear shots. We're a 10:1 plaction wheel swerve drive, btw.

[Aren_Hill]

Originally Posted by Jeffy

If you want an omnidirectional drivetrain, it appears that swerve would be the best because it gives omnidirectional motion with better traction and without the power loss of mecanum.
However, our meccanum drivetrain has served us very well this year. When we decided we wanted to have omni directional capabilites they were our best option because our team is not capable of building a successful swerve in 2 weeks.
The mecanum does have (atleast) one advantage, swerve has a lag while the pods turn. One other might be weight. If you direct drive 6" mecanums then it should surely be lighter than 4 (or 6) swerve pods, chain, and sterring assemblies. This did not prove to be the case for us this year because we are chain driving 4 8" wheels with 4 toughboxes.

For a game like breakaway where pushing isn't a factor unless your playing a defensive strategy, you really can't go wrong with either.

weight of an 8" AM mecanum = weight of one of our swerve modules, without making them anorexic

The weight of a swerve system will come down iteration by iteration, but the same goes for a solid tank system which can go much lower.

[Tom Line]

Originally Posted by sidkulk

I think the choice between mecanum and swerve lies in where your robot is best suited to play (offense/midfield/defense).

Offense: Swerve
From watching quite a few matches, swerve seems alot better suited to collect balls and maneuver them into the goal.

Midfielf: Swerve
When your playing the midfield balls constantly keep entering, so you need to be able to quickly "pick up" balls from your zone. And if your in the midfield, theres a higher chance of you needing to go over the bump. So if you use mecanum it seems you need to drive straight to go over on mecanum, but you can go also sideways with swerve over the bump

Defense: Mecanum
Mecanum seems better here because its alot easier to get from goal to goal and just block the goal from other robots scoring.

No - at least not by our scouting methods. Mecanum robots are immediately removed from our defensive pic list, as are robots with slick wheels / omni wheels. A decently geared robot with traction wheels will have no problem moving a robot with slick/omni or mechanum out of their way and scoring.

Mechanum are a neat idea (as are omni wheels), but once you bring robot to robot contact into the equation, I'd much rather have robots with traction that won't get pushed out of the way easily.

Regarding any lag time with swerve modules: If you have it programmed correctly, your swerve modules should never have to turn more than 90 degrees from any given point. When you keep in mind that a tank drive has to "turn" before it drives forward, there really is no lag in a well-done swerve drive when compared to a tank drive. When you take into account acceleration time, there really isn't any lag in a swerve compared to a mechanum either.

You may want to note, however, that except for a few teams, most teams do NOT do swerve every year. Even teams that have done swerve, generally don't repeat it much. That's because it takes so much time, machining, programming etc to make it work well.

Swerve is that thing that every team has to try at least once. They try it, they may win a couple engineering awards with it: then most teams rarely do it again.

[alicen]

Originally Posted by Tom Line

No - at least not by our scouting methods. Mecanum robots are immediately removed from our defensive pic list, as are robots with slick wheels / omni wheels. A decently geared robot with traction wheels will have no problem moving a robot with slick/omni or mechanum out of their way and scoring.

Mechanum are a neat idea (as are omni wheels), but once you bring robot to robot contact into the equation, I'd much rather have robots with traction that won't get pushed out of the way easily.

I have to disagree. This is the third year my team has done mecanum drive, and we were able to play defense well. Defense doesn't necessarily have anything to do with pushing if you're maneuverable enough.

If you want to find an holonomic drive that also has pushing power, you might try over the summer looking into mecanums that have a mechanism which locks all the mech rollers.

[davidthefat]

What about a 2 wheel drive? It can turn very tight and stuff